A guide to wireless antenna selection
It is important wireless transmissions are reliable regardless of situation. A five-step plan for effective antenna selection is highlighted.
Learning Objectives
- Wireless communications must be reliable regardless of setting. Picking the right antenna is crucial.
- Considering hardware, signal strength, distance and more are among the things people need to keep in mind when picking an antenna.
- It’s important to keep international standards in mind, as well, because they are designed to prevent interference.
Wireless insights
- It’s important the equipment behind a wireless telemetry application is reliable and designed to work regardless of setting.
- Users can learn a lot during the site survey, which will provide the user with a great deal of information on what is and isn’t needed.
A wireless telemetry application is only as good as the antenna system. Whether it’s a radiological system in a nuclear plant, an industrial alarm, or even a utility gas or water meter, it’s important that the signals are reliably transmitted and received.
Step 1: Consider the radio application itself. The reason why companies will have chosen to transmit the signals wirelessly is because it’s not feasible to lay cable over a long distance, or there isn’t already existing cabling on site. It’s also important, then, to consider where the signal needs to come from and to – is it a single point-to-point network, a multiple point, or peer-to-peer network?
Step 2: Carry out the site survey. The time-tested visual survey is still one of the best methods to do this. It is referred to as a line-of-sight survey, and it means just that. The user physically stands at point A and look towards point B, visually checking for obstructions and buildings. Also, consider any future obstructions or weather interference issues at this stage.
Step 3: Determine the distance between the two points. If it’s a very short distance, it could be judged by eye, but the important thing to remember is radio transmission distance is finite, based on factors such as the power of the transmitter, the sensitivity of the receiver, the type of antenna being used and the weather conditions. These factors will determine whether the user gets a good signal or not.
Step 4: Run a test for signal strength. Setup a test rig by placing the actual monitoring equipment intended for use in this project at point A and point B and run a simulation to allow the two pieces of kit to communicate with each other. Using a general-purpose radio test set up is a good alternative.
Step 5: Consider the antenna hardware. The two major types of antennas are omnidirectional and directional. Omnidirectional antennas are useful if there is a multipoint setup, for example a water or gas telemetry application, where users need to receive signals at one central receiver from many transmitters. The other type is a directional antenna, which is ideal for single transmission devices, such as an outlying telemetry device sending its signal back to a central mast.
It is important to note that in most countries around the world, to prevent interference between different users, the radio spectrum is regulated using licensed and unlicensed frequency bands. However, regardless of which is being used, the gain of the antenna cannot result in exceeding the effective radiated power (ERP) allowed on that frequency band. On the 868 Mhz frequency, in the UK for example, the maximum ERP for short range devices and wideband devices is limited to 25 dBm with a duty cycle of 10%.
In other parts of the world, this can differ. For example, South Africa falls into the same EMEA zone and largely follows the same radio standards, although short range devices in the country must register type-approval for radio devices with the Independent Communications Authority of South Africa (ICASA). At the same time, Australia, New Zealand and Asia are considered a separate region and have their own standards.
Antenna selection may at first seem like a daunting prospect, but by following these simple steps, you can ensure your wireless telemetry application has a reliable and strong signal.
Ian McNeilage is engineering manager at Omniflex. This originally appeared on Control Engineering Europe’s website. Edited by Chris Vavra, web content manager, Control Engineering, CFE Media and Technology, cvavra@cfemedia.com.
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Keywords: wireless, antenna selection
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